This chapter introduces two techniques for documenting business processes- Data Flow Diagrams (DFD's) and System Flowcharting (SFC). It discusses how to read these documents, their purpose, and guidelines for creating DFD's and SFC's from narratives (see discussion)
Data Flow Diagrams:
Types of Dataflow Diagrams (define and explain the differences):
Context Diagram - top level DFD, is a representation of the system and presents all activites as a single bubble.
Physical - A graphical representation of a system showing the system's internal and external entities and the flows of data into and out of these entities. Specifies the where, how, and by whom a system's processes are accomplished.
Logical - A graphical representation of a system showing the system's processes, data stores, and the flows of data into and out of the processes and data stores. Concentrates on the functions that a system performs rather than how data is transmitted. Describes "WHAT" the system is doing.
Levels of Dataflow Diagrams:
Context: a top-level physical DFD that illustrates the entire system and all of its internal activities in one bubble, with data flows moving between the system and external entities. A context DFD shows the broader picture of the information system.
Level-0: the next level of detail of a DFD below a context DFD; a logical DFD that shows the data flows between internal processes and data stores within a single bubble of a context DFD.
Level-1: the next level of a DFD below a Level-0; a logical DFD that shows the data flows between internal processes and data stores within a single bubble of a level-0 DFD.
Level-x (How low can you go?) Functional Primitive: lowest level (the bottom-most bubble).
Balanced Data Flow Diagram set: this occurs when two or more DFDs have the same external data flows. Only balanced DFD sets are correct.
Data Flow Diagram Symbols:
Bubble (Physical or Logical) - depicts an entity or a process within which incoming data flows are transformed into outgoing data flows
Arrow - represents a pathway for data. The direction of the arrow reflects the direction in which the data is flowing, i.e. from an entity or process to an entity or process.
Box - External entity symbol - portrays a source or a destination of data outside the system
Open-ended Rectangle - Data store symbol - represents a place where data are stored
Systems Flowcharts
Systems Flowchart (SFC): a graphical representation of a business process, including both its information (inputs and outputs, data processes and storage) and operations (people, equipment, structure and activities) processes. A single SFC gives a more complete picture of a process than a single DFD since it offers both a physical and a logical view of the process.
Common Systems Flowcharting Routines:
Preparing Systems Documentation:
Table of Entities and Activities (describe the steps for creation):
To begin your table, go through the narrative line by line and circle each activity (mainly verbs) being performed. An activity is any action being performed by an internal or external entity. Activities examples: send, transform, file, retrieve. For each activity, there must be an entity that performs the activity. List each activity in the order that it is performed, regardless of the sequence in which it appears in the narrative. List the activity, along with the name of the entity that performs the activity. After you have listed all activities, consecutively number each activity. Group the logical activities together.
Rules of DFD Construction:
All data flows must begin and/or end at a process since data flows either initiate or result from a process
A process cannot have only outputs; this results in a "miracle"
A process cannot have only inputs; this results in a "black hole"
The inputs to a process must be a sufficient to produce the outputs from the process. Otherwise, there it is a "gray hole"
All data stores must be connected to at least one process.
A data store cannot be connected to a source or sink.
A data flow can have only one direction of flow. Multiple data flows to and/or from the same process and data store must be shown by separate arrows.
If the exact same data flows to two separate processes, it should be represented by a forked arrow.
Data cannot flow directly back into the process it has just left.
Documenting Information Systems:
This chapter introduces two techniques for documenting business processes- Data Flow Diagrams (DFD's) and System Flowcharting (SFC). It discusses how to read these documents, their purpose, and guidelines for creating DFD's and SFC's from narratives (see discussion)Data Flow Diagrams:
Types of Dataflow Diagrams (define and explain the differences):
Levels of Dataflow Diagrams:
Data Flow Diagram Symbols:
Systems Flowcharts
Systems Flowchart (SFC): a graphical representation of a business process, including both its information (inputs and outputs, data processes and storage) and operations (people, equipment, structure and activities) processes. A single SFC gives a more complete picture of a process than a single DFD since it offers both a physical and a logical view of the process.Common Systems Flowcharting Routines:
Preparing Systems Documentation:
Table of Entities and Activities (describe the steps for creation):
To begin your table, go through the narrative line by line and circle each activity (mainly verbs) being performed. An activity is any action being performed by an internal or external entity. Activities examples: send, transform, file, retrieve. For each activity, there must be an entity that performs the activity. List each activity in the order that it is performed, regardless of the sequence in which it appears in the narrative. List the activity, along with the name of the entity that performs the activity. After you have listed all activities, consecutively number each activity. Group the logical activities together.
Rules of DFD Construction:Additional Resources:
Business Processes: IBM explains why documentation is worth the investment
http://www.research.ibm.com/journal/sj/381/millet.html : This article is also interesting. It explains a researchers desire to adapt DFD's, making them easier to create and read.